Field of the Invention
The present invention relates to an electronic apparatus in which a plurality of control chips are cascade-connected.
Description of the Related Art
As an information output apparatus for a wordprocessor, personal computer, facsimile apparatus, or the like, a printer which records information such as desired characters or images on a sheet-like recording medium such as paper or a film is widely used.
Various methods are known as a recording method of the printer. An inkjet method is recently particularly attracting attention among others because non-contact recording can be performed on a recording medium such as paper, color recording is easy, and the operation is very silent. As a configuration of this inkjet method, a serial inkjet recording apparatus is generally widely used from the viewpoints of a low cost, the ease of downsizing, and the like. This apparatus includes a recording head for discharging ink in accordance with a recording instruction, and performs recording by scanning the recording head back and forth in a direction perpendicular to the feed direction of a recording medium such as paper.
The inkjet recording apparatus as described above further increases the resolution of image recording by decreasing the ink discharge amount per dot while increasing the integration density of nozzles for discharging ink droplets. Also, various techniques have been developed to obtain a higher image quality. For example, in addition to the four basic color inks (cyan, magenta, yellow, and black), light-colored inks obtained by decreasing the dye concentrations of the four basic inks and spot color inks such as red, green, and blue are recorded at the same time.
On the other hand, the recording speed may decrease if the image quality keeps increasing. However, good results are beginning to be obtained for this problem by increasing the number of recording elements, increasing the driving frequency, adopting a recording technique such as bidirectional recording which performs recording when the recording head scans back and forth, and increasing the conveyance speed of a recording sheet.
Also, for the purpose of further increasing the speed of the inkjet recording apparatus, cases in which a system is configured by connecting a plurality of controller chips (to be simply referred to as chips hereinafter) and various processes and terminal functions are dispersed are increasing.
The system configured by connecting a plurality of chips can be obtained by preparing chips specialized in individual functions. However, there is a case in which if the system can be configured by using identical chips, this is desirable in both the development load and cost. When configuring the system by using a plurality of chips, how to share and manage errors which can occur in these chips is important. Especially when a CPU for controlling the system becomes unable to perform appropriate control, it becomes impossible to normally control the recording head and motor, and this may lead to a failure of the main body. To avoid this inconvenience, a monitoring method which monitors the CPU by using a watchdog timer and automatically resets the system if a problem arises is generally often used.
When the system is configured by a plurality of chips, however, if a CPU in a given chip becomes unable to perform proper control, how to share the state by the individual chips and how to safely stop the whole system are important. By assuming a state like this, a method of monitoring at least two microcontrollers by using one watchdog is disclosed in, for example, literature: Japanese Patent Laid-Open No. 2013-541089. The watchdog is allocated to a first microcontroller, and monitors the notification of a message from the first microcontroller within the time interval of a predetermined period. A message notified to the watchdog by the first microcontroller contains a contribution formed as a result of communication between the first microcontroller and a second microcontroller connected to the first microcontroller. In this disclosed method, the watchdog checks, based on the contribution, whether the second microcontroller is correctly operating.
In this literature, however, a configuration in which one watchdog timer monitors a plurality of controllers is possible, but whether the second controller is normally operating can be determined by only communication with the first controller. If an error occurs in the first controller, the first controller cannot communicate with the second controller any longer, so the second controller may become uncontrollable.
If the occurrence of an error can be shared in the whole system, the system can perform appropriate processing corresponding to the error. For example, if the reason for the incapability of communication is that the communication is only momentarily interrupted by the influence of static electricity or the like, it is only necessary to reestablish the communication by performing a retry operation or the like. On the other hand, if the communication is impossible because the watchdog timer operates and resets the controller, it is necessary to rapidly stop power supply to the motor, head, and the like consuming high power, and set the whole system in a safe state.
Accordingly, the system configured by using a plurality of controllers requires a technique by which if an error occurs for some reason in a specific controller and the watchdog timer operates, the whole system properly shares this information.